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Humans are living longer than ever, a life-span extension that
occurred more rapidly than expected and almost solely from
environmental improvements as opposed to genetics, researchers
said today (Oct. 15).

Four generations ago, the average Swede had the same probability
of dying as a hunter-gatherer, but improvements in our living
conditions through medicine, better sanitation and clean drinking
water (considered "environmental" changes) decreased mortality
rates to modern levels in just 100 years, researchers found.

In Japan, 72 has become the new 30, as the likelihood of a
72-year-old modern-day person dying is the same as a 30-year-old
hunter-gatherer ancestor who lived 1.3 million years ago. Though
the researchers didn't specifically look at the United States,
they say the
trends are not country-specific and not based in genetics.

Quick jump in life span

The same progress of decreasing average
probability of dying at a certain age in hunters-gatherers
that took 1.3 million years to achieve was made in 30 years
during the 21st century.

"I pictured a more gradual transition from a
hunter-gatherer mortality profile to something like we have
today, rather than this big jump, most of which occurred in the
last four generations, to me that was surprise," lead author
Oskar Burger, postdoctoral fellow at the Max Planck Institute for
Demographic Research in Germany, told LiveScience.

Biologists have
lengthened life spans of worms, fruit flies and mice in labs
by selectively breeding for old-age survivorship or tweaking
their endocrine system, a network of glands that affects every
cell in the body. However, the longevity gained in humans over
the past four generations is even greater than can be created in
labs, researchers concluded. [ Extending
Life: 7 Ways to Live Past 100 ]

Genetics vs. environment

In the new work, Burger and colleagues analyzed previously
published mortality data from Sweden, France and Japan, from
present-day hunter-gatherers and from wild chimpanzees, the
closet living relative to humans.

Humans have lived for an estimated 8,000 generations, but only in
the past four have mortalities decreased to modern-day levels.
Hunter-gatherers today have average life spans on par with wild
chimpanzees.

The research suggests that while genetics plays a small role in
shaping human
mortality, the key in driving up our collective age lies with
the advent of medical technologies, improved nutrition, higher
education, better housing and several other improvements to the
overall standards of living.

"This recent progress has been just astronomically fast compared
to what we made since the split from chimpanzees," Burger said.

Most of the brunt of decreased mortality comes in youth: By age
15, hunters and gatherers have more than 100 times the chance of
dying as modern-day people.

What's next?

"In terms of what's going on in the next four generations, I want
to be very clear that I don't make any forecasts," Burger said.
"We're in a period of transition and we don't know what the new
stable point will be."

However, some researchers say that humans may have maxed out
their old age.

"These mortality curves (that show the
probability of dying by a certain age), they are now
currently at their lowest possible value, which makes a very
strong prediction that life span cannot increase much more,"
Caleb Finch, a neurogerontology professor at the University of
Southern California who studies the biological mechanisms of
aging, told LiveScience in an email.

Further, Finch, who was not involved in the current study, argues
that environmental degradation, including climate change and
ozone pollution, combined with increased obesity "are working to
throw us back to an earlier phase of our improvements, they're
regressive."

"It's impossible to make any reasonable predictions, but you can
look, for example, in local environments in Los Angeles where the
density of particles in the air predict the rate of heart disease
and cancer," Finch said, illustrating the link between the
environment and health.

The study is detailed today (Oct. 15) in the journal Proceedings
of the National Academy of Sciences.

Editor's Note: This article was updated to
clarify the difference between life span and mortality rate.